Signal level detection apparatus and detection method, and signal level display apparatus

ABSTRACT

A signal level detector to detect the level of 1-bit digital signal is provided. It includes a level detector ( 12 ) supplied with a sequence of 1-bit digital signals decoded by an audio decoder ( 5 ) and which counts the number of 0 (zeros) or 1 (ones) included in the row of a predetermined number n of 1-bit digital signals to detect the level of the 1-bit digital signal, and an indication unit ( 13 ) to indicate the signal level detected by the level detector ( 12 ).

TECHNICAL FIELD

[0001] The present invention generally relates to a signal leveldetecting apparatus and method, and more particularly to an apparatusfor, and a method of, detecting the level of a 1-bit digital signalobtained by the delta-sigma modulation, and an apparatus for indicatingthe signal level detected by the signal level detector.

BACKGROUND ART

[0002] In the conventional compact disc (CD), the sampling frequency fsis about 44.1 kHz and the PCM method is used to record one sample as16-bit digital audio data for each channel. There has been proposed aso-called super audio compact disc (SACD) in which a 1-bit audio streamdata is recorded with a very high sampling frequency generated by theDSD (direct stream digital) method (for example, a frequency 64 timeshigher than the sampling frequency fs in the ordinary CD).

[0003] By oversampling delta-sigma modulation of an input signal with 64fs, there is generated a 1-bit audio digital signal. Hereupon, the 1-bitaudio digital signal is decimated into a multi-bit PCM code in the CDusing the PCM method. In the SACD using the DSD method, however, the1-bit audio digital signal is recorded directly to the SACD.

[0004] The frequency band of the 1-bit audio signal recorded to the SACDis about 100 kHz. This is rather wider than the frequency band of thesignal in the PCM method adopted in the CD.

[0005] In playback of the SACD having recorded therein the same audiosignal in such a wide frequency band as in the CD, sound components ofrelatively low frequencies can be reproduced to be audible to the humanears. For example, even when the SACD is played back in a player havingno ample acoustic-pressure frequency response, such as a home audioplayer, the sound recorded in the SACD can be reproduced to be audibleto the human ears. However, the human ears can hardly hear soundcomponents of high frequencies, such as 20 kHz or higher, reproducedfrom the SACD. When an audio signal in a wide band including highfrequencies is reproduced from the SACD, sound components thereof in thelow frequency band are audible to the human ears but sound components inthe high frequency band are not audible to the human ears.

[0006] When reproducing an audio signal from a sound source including upto sound components of high frequencies such as about 100 kHz and whichhas an acoustic level of sound components in a high frequency band notaudible to the human ears is higher than that of sound components in alow frequency band, raising the reproduction level of an audio playerused for the audio signal reproduction, with the ability of the humanears taken in consideration, for the sound components in the lowfrequency band to be audible to the human ears at a sufficiently highacoustic pressure level, will result in an elevated acoustic pressurelevel of the sound components in the high frequency band for the highreproduction level. Since the human ears cannot hear any soundcomponents in the high frequency; band, the reproduction level maypossibly be raised above the capability of the audio player with theresult that the power amplifier and speaker of the audio player islikely to be greatly loaded and damaged as the case may be.

[0007] Therefore, a function to monitor the sound level of soundcomponents difficult to capture by the human ears should be provided ina player designed to reproduce audio signals in a wide band includingfrom a low frequency to a high frequency such as 100 kHz, such as audiosignals recorded to the SACD, or in an recorder to record such audiosignals and an apparatus to produce a medium such as a compact disc orthe like.

[0008] On the other hand, different from the multi-bit digital signalobtained by the conventional PCM method, the 1-bit digital signalobtained by the delta-sigma modulation includes also frequencycomponents beyond the audio band of frequencies audible to the humanears. So, the level of the 1-bit digital signal cannot be known if leftas it is. Conventionally, to know the level of a signal, only anecessary frequency component of the signal are extracted using adigital filter and the level of the signal is indicated based on thedata thus extracted.

[0009] When the digital filter is used, however, different outputs maypossibly result from the same input signal depending upon how thedigital filter has been designed, namely, depending upon the type,factor and computing word length thereof. For example, since it isdifficult to determine the level of the signal uniquely, indication ofthe same signal supplied to a player will possibly vary from oneapparatus to another. Since the digital filter uses a multiplier andadder, its circuit is likely to be complicated and large in scale, whichwill cause a large manufacturing cost and increased power consumption ofthe circuit.

[0010] Also, if the digital filter is strictly designed for thecompletely same output from an input, it will be less flexible inperformance and manufacturing cost so that the product design will bedifficult in practice.

DISCLOSURE OF THE INVENTION

[0011] Accordingly, the present invention has an object to overcome theabove-mentioned drawbacks of the related art by providing an apparatusfor, and a method of, detecting the level of a 1-bit digital signal by asimple circuit construction.

[0012] The present invention has another object to provide a signallevel indication apparatus for indicating the signal level detected bythe signal level detector and capable of solving the conventionalproblem that the level indication of a 1-bit digital signal varies fromone type the apparatus from another.

[0013] The above object can be attained by providing a signal leveldetector including according to the present invention:

[0014] a counting means sequentially supplied with 1-bit digital signalsobtained by the delta-sigma modulation and which counts the number ofzeros (0) or ones (1) in the 1-bit digital signal row including apredetermined number of 1-bit digital signals.

[0015] In the above signal level detector, the level of the 1-bitdigital signal is detected based on the number of zeros (0) or ones (1)counted by the counting means.

[0016] Also the above object can be attained by providing a signal leveldetecting method including according to the present invention steps of:

[0017] sequentially receiving 1-bit digital signals obtained by thedelta-sigma modulation and counting the number of zeros (0) or ones (1)in the 1-bit digital signal row including a predetermined number of1-bit digital signals; and

[0018] detecting the level of the 1-bit digital signal based on thenumber of zeros (0) or ones (1) counted in the counting step.

[0019] Also the above object can be attained by providing a signal levelindication apparatus including according to the present invention:

[0020] a counting means sequentially supplied with 1-bit digital signalsobtained by the delta-sigma modulation and which counts the number ofzeros (0) or ones (1) in the 1-bit digital signal row including apredetermined number of 1-bit digital signals; and

[0021] means for indicating the signal level detected based on thecounting result supplied from the counting means.

[0022] These objects and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription of the best mode for carrying out the present invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a block diagram of an optical disc player according tothe present invention.

[0024]FIG. 2 is a block diagram of the delta-sigma modulator.

[0025]FIG. 3 is a block diagram of the level indication apparatusincorporated in the optical disc player according to the presentinvention.

[0026]FIG. 4 is a block diagram of the moving average filter.

[0027]FIG. 5 shows the frequency response of the moving average filter.

[0028]FIG. 6 shows the number m of ones (1) in a sequence of n data(n=28) and the signal level A of the data.

[0029]FIG. 7 is a block diagram of a variant of the level indicationapparatus according to the present invention.

[0030]FIG. 8 is a block diagram of an optical disc recorder according tothe present invention.

[0031]FIG. 9 is a block diagram of an optical disc editing apparatusaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0032] Some embodiments of the present invention will be describedherebelow with reference to the accompanying drawings.

[0033] Referring now to FIG. 1, there is illustrated in the form of ablock diagram an embodiment of the optical disc player according to thepresent invention, in which the level indication apparatus is provided.

[0034] For building up an optical disc player from a disc playercompatible with a super audio compact disc (SACD) as a recording medium,or an optical disc playing system which uses a digital/analog (D/A)converter, amplifier, etc. along with the disc player, a level metershould desirably be provided which can monitor also sounds of highfrequencies which cannot be captured by the human ears. To build up thedisc player using the SACD or the optical disc playing system as aconsumer apparatus, a level indication apparatus such as the level meterhas to be provided to avoid that the disc player and disc plating systemwill be expensive.

[0035] To meet the above requirements, the optical disc player accordingto the present invention incorporates a level indication apparatus 11 asshown in FIG. 1. The level indication apparatus 11 indicates the levelof a 1-bit audio signal reproduced from an SACD 1. The construction andfunction of the level indication apparatus 11 will be described indetail later.

[0036] Prior to explaining the optical disc player according to thepresent invention in detail, the SACD 1 as a recording medium played inthe optical disc player will first be explained.

[0037] The SACD 1 has recorded directly therein the 1-bit audio signalobtained by the delta-sigma modulation of the audio signal from a soundsource. FIG. 2 shows the delta-sigma modulator to generate the 1-bitaudio signal. As shown, the delta-sigma modulator includes an adder 15,1-bit quantizer 16 and an integrator 17. In the delta-sigma modulator,the adder 15 determines a difference (delta: Δ) between an analog signalsupplied via an input terminal 15 a of the adder 15 and an integratedvalue (sigma: Σ) of a 1-bit output signal and supplies it to the 1-bitquantizer 16. The output signal consists of logical zeros (0) andlogical ones (1) which represent −1 and +1, respectively, as actualvalues. The integrator 17 accumulates 1-bit output signals and outputsan accumulated value which follows up with the value of the analog inputsignal. Each time the 1-bit quantizer 16 generates one bit, it increaseor decreases the accumulated value by one. The sampling frequency is sohigh as to generate a string of output bits whose accumulated value willfollow up the analog input signal. The sampling frequency is 64 fs (64times higher than fs (=44.1 kHz), for example. A 64 fs, 1-bit digitalaudio signal is provided at an output terminal 15 b of the adder 15. The64 fs, 1-bit digital audio signal output from the delta-sigma modulatoris recorded to the SACD 1.

[0038] In the optical disc player shown in FIG. 1, the SACD 2 is rotatedby a spindle motor 7 at a constant linear velocity (CLV), for example.The SACD 1 rotated by the spindle motor 7 is scanned over a signalrecording area thereof by a read laser light emitted from a light sourceprovided in an optical pickup 2 moved radially of the SACD 1. The laserlight incident upon the SACD 1 and reflected from the latter is detectedbu a light detector provided in the optical pickup 2 to read the 1-bitaudio signal recorded on the SACD 1. The signal read by the opticalpickup 2 is supplied to an RF amplifier 3. An RF signal output from theRF amplifier 3 is supplied to a front end processor 4 where it willundergo demodulation and error correction to generate sector data havinga fixed length of 2064 bytes, for example. The sector data is suppliedto an audio decoder 5 provided downstream of the front end processor 4.

[0039] The audio decoder 5 receives, from the front end processor 4, thesector data having the fixed length of 2064 bytes one by one, analyzesan audio header beginning from the top of each sector, and records thedata to each block of an internal or external memory in units of{fraction (1/75)}-sec frame.

[0040] The data recorded in units of frame in each block of the internalor external memory is supplied to a compression decoder (not shown),provided in the audio decoder 5, where it will be decoded. The decodeddata is faded as necessary in a fader, converted by a D/A converter 8into an analog audio signal and then supplied from an output terminal 9to an external amplifier, speaker, etc. The audio decoder 5 supplies thedecoded 1-bit audio signal to the level indication apparatus 11 as well.

[0041] The RF amplifier 3 generates also a tracking error signal andfocus error signal from the read signal detected by the optical pickup 2and supplies these signals to a servo signal processing circuit 6. Basedon the tracking and focus error signals supplied from the RF amplifier3, the servo signal processing circuit 6 moves an objective lens whichgathers and directs the reading laser light emitted from the opticalpickup 2 upon the signal recording surface of the SACD 1. As drivecurrents corresponding to the focus and tracking error signals,respectively, are supplied to an objective lens driving mechanism suchas an actuator holding the objective lens and the like, the objectivelens is moved in a focusing direction parallel to the optical axisthereof and in a tracking direction orthogonal to the optical axis. Asthe objective lens is thus moved based on the focus and tracking errorsignals, the reading laser light emitted from the light source in theoptical pickup 2 is focused onto the signal recording surface of theSACD 1 and controlled to follow up a recording track formed on the SACD1. Also, the servo signal processing circuit 6 controls the spindlemotor 7 to rotate.

[0042] The audio decoder 5, servo signal processing circuit 6, etc.operate under the control of a controller 10. The controller 10 has auser's operation unit 14 connected thereto. The controller 10 includes alevel detector 12 which will be described in detail later.

[0043] The level indication apparatus 11 includes the level detector 12to detect the level of a 1-bit digital signal supplied from the audiodecoder 5, and an indicator unit 13 to indicate the signal leveldetected by the level detector 12.

[0044] The level detector 12 is supplied with a sequence of 1-bitdigital signals read from the SACD 1, and counts the number of zeros (0)or ones (1) included in a 1-bit digital signal row consisting of anumber n of 1-bit digital signals to detect the level of the 1-bitdigital signal.

[0045]FIG. 3 shows in detail the construction of the level indicationapparatus 11 including the level detector 12 and indicator unit 13.

[0046] The level detector 12 includes a shift register 23 to store the1-bit digital signal row, counter 24 to count zeros (0) and ones (1) inthe 1-bit digital signal row, and a comparator 25 to compare the resultof counting supplied from the counter 24 with a built-in conversiontable. The indicator unit 13 includes four indicators 13 ₁, 13 ₂, 13 ₃and 13 ₄, for example, which turn on correspondingly to the result ofcomparison supplied from the comparator 25. The shift register 23 shiftsthe 1-bit audio signal supplied from the audio decoder 5 via an inputterminal 21 to store a 1-bit digital signal row including apredetermined number n of 1-bit digital signals. The counter 24 countsthe number of zeros (0) and ones (1) included in the 1-bit digitalsignal row stored in the shift register 23. The comparator 25 comparesthe result of counting supplied from the counter 24 with values in theconversion table stored in a memory 26 which will be described later toprovide a level A (dB) for determining which one of the indicatorsincluded in the indicator unit 13 turns on.

[0047] The level indication apparatus 11 constructed as above functionsas will be described below:

[0048] First, the shift register 23 and counter 24 are reset by a resetsignal supplied from the controller 10 via a terminal 22. After thereset signal is cleared, the counter 24 monitors the output of the shiftregister 23 each time a 1-bit audio signal is supplied from the inputterminal 21 to count how many zeros (0) and ones (1) are in the shiftregister 23.

[0049] The data counted by the counter 24 is sent to the comparator 25which will locate a value of the level A (dB) based on the data andreferring to the conversion table in the memory 26 to thereby determinewhich one of the indicators is to be turned on.

[0050] The level detector 12 functions as will be discussed below:

[0051] The more positive the analog input waveform goes, the more timesthe 1-bit digital signal generated by the delta-sigma modulator isoutputted as one (1). On the other hand, the more negative the analoginput waveform goes, the more times the 1-bit digital signal isoutputted as zero (0). At the zero point, zeros (0) and ones (1) areoutputted almost alternately, namely, the zeros (0) and ones (1) areoutputted the same times. Thus, the variation in amplitude of the analoginput waveform is represented by densities of the ones and zeros,respectively, like a pulse density.

[0052] Therefore, a row of data in which the same numbers of ones (1)and zeros (0) are listed, such as “0101010101010101010101010101”, is “0”in the PCM method. Similarly, a row of data including more ones (1) thanzeros (0) indicates a positive signal level, while a row of dataincluding more zeros (0) than ones (1) indicates a negative signallevel.

[0053] Further, a row of data all being “1” indicates a largest positivesignal level, while a row of data all being “0” indicates a largestnegative signal level.

[0054] Assume here that a sequence of n data includes a number m of ones(1). The modulation factor η for this signal is represented by:

η=|2m−n|/n

[0055] When m=n or n=0, for example, the modulation factor η is 100%.When m=(¾)n or (¼)n, the modulation factor η is 50%. When m=n/2, themodulation factor η is 0%.

[0056] Since the sound level is considered to be proportional to themodulation factor η, the sound level A is represented as follows on theassumption that the modulation factor η of 50% corresponds to 0 dB:

Level A(dB)=20log{|2(2m−n)|/n}

[0057] Note that to count the number of ones (1) included in a data rowhaving a length n as above is to use one moving average filter stagehaving the length n as shown in FIG. 4. The moving average filterincludes a number n of flip-flops FF 51 ₁, 51 ₂, 51 ₃, . . . , 51_(n-2), 51 _(n-1) and 51 _(n) to shift a data input Din A, and an adder52 to add together outputs from the number n of FFs to provide a movingaverage filter output Fout.

[0058] Note that when the sampling period of the data row is 44.1kHz×64=2.8244 MHz used in the super audio CD (SACD) and the filterlength n=28, the frequency response of the moving average filter is asshown in FIG. 5. That is, the moving average filter shown in FIG. 4 isto lower the signal level by about 3 dB at a frequency of about 50 kHz,namely, a filter for about 100 kHz. Namely, by counting the number ofzeros (0) or ones (1) included in a sequence of 28 data, it is possibleto simply examine the signal level at the frequency of about 100 kHz.

[0059]FIG. 6 shows the relation between a number m of ones (1) when thenumber of data in a sequence is n=28 and the signal level value A,namely, the content of the conversion table. The signal level value A isa logarithmic value.

[0060] When the counter by the counter 24 in the level detector 12 shownin FIG. 3 is over 21 or under 7, the indicator 13 ₂ in the indicatorunit 13 is turned on. The indicator 132 corresponds to +0 dB, whichmakes it possible to know that the input signal level is over +0 dB.

[0061] As having been described above, since the optical disc player forreproducing 1-bit digital signals obtained by the delta-sigma modulationuses a modulation factor for a signal to examine the level of thesignal, the level indication apparatus 11 shown in FIG. 3 needs nomultiplier and adder and thus can be designed simpler. Because of thesimplified circuit, the level indication apparatus 11 can bemanufactured with less costs and can operate with less powerconsumption. The level indication apparatus 11 according to the presentinvention may not be any dedicated circuit but may be formed from a CPUand its software. Thus, the construction itself can be designed notcomplicated. Further, since the accuracy of signal processing dependsupon the CPU and its software, a signal level can be determineduniquely.

[0062] By providing the level indication apparatus 11 in the opticaldisc player according to the present invention, it can be avoided thatwhen the same music is reproduced by a plurality of the optical discplayers, the level of the music data is indicated varying from oneplayer type to another. Also, by selecting an appropriate parameter forthe modulation factor, it is possible to match the modulation factorwith an intended frequency band.

[0063]FIG. 7 shows in detail the construction of a variant of the levelindication apparatus 11. The level indication apparatus is generallyindicated with a reference 40.

[0064] In the level indication apparatus 40, the level detector 12further includes an exclusive-OR circuit 27 and counter 28 providedbetween the shift register 23 and comparator 25. The exclusive-ORcircuit 27 makes exclusive-OR of 1-bit digital signal supplied from theinput terminal 21 and an output from the shift register 23. The counter28 counts outputs from the exclusive-OR circuit 27.

[0065] The level indication apparatus 40 constructed as above functionsas will be outlined below:

[0066] First, a reset signal supplied from the controller 10 is suppliedto the shift register 23 and counter 28 via the terminal 22. The resetsignal will reset the shift register 23 to“0101010101010101010101010101” which indicates zero (0) of the 1-bitdigital audio signal. The counter 28 is set to the number of ones (1) inthe 1-bit digital audio signal (14 in this case). After the reset signalis cleared, the exclusive-OR circuit 27 make exclusive-OR of 1-bitdigital audio signal supplied from the input terminal 21 and output fromthe shift register 23. When the output from the exclusive-OR circuit 27is zero (0), the supplied 1-bit digital signal and output from the shiftregister 23 are equal in value to each other, which means that in theshift register 23, the number of zeros (0) is equal to that of ones (1).In this case, the count in the counter 28 has not to be changed. Whenthe output from the exclusive-OR circuit 27 is one (1), it is determinedthat the supplied 1-bit digital signal and output from the shiftregister 23 are different in value from each other. Thus, when theoutput from the shift register 23 is zero (0), the count in the counter28 is increased by one. When the output is one (1), the count in thecounter 28 is decreased by one. By examining the input to, and outputfrom, the shift register in the above way, it is possible to know thenumbers of zeros (0) and ones (1) without examining, at every time, theentire content of the shift register 23 as in the level detector 12constructed as in FIG. 3.

[0067] In the optical disc player in which 1-bit digital signalsobtained by the delta-sigma modulation are used, when the number ofzeros (0) or ones (1) is known, the level indication apparatus 11 shownin FIG. 3 can detect the level of the signal with the use of amodulation factor for the signal and indicate it. That is, theaforementioned effect can be attained with the reduction of the amountof data processing.

[0068] Next, a second embodiment of the present invention will bedescribed.

[0069] The second embodiment is an application of the present inventionto an optical disc recorder incorporating the level indication apparatusaccording to the present invention.

[0070] At a site such as a recording studio, it is necessary to recordsignals while always monitoring the signal state. The signal-statemonitoring is required because too high a level of a signal supplied toa recorder such as an optical disc recorder will possibly saturate thesignal to be recorded, distort a sound to be recorded or damage therecorder in some cases. Reversely, when a signal supplied to therecorder is at too low a level, the signal will be recorded with a poorsound quality (with no dynamic range). Therefore, the recording levelindication apparatus should be accurate since the recording levelgreatly affects the quality of the recording sound. That is, the levelindication apparatus has to provide the same level indication for thesame signal independently of the recording time, recording site andrecorder type.

[0071] Referring now to FIG. 8, there is illustrated in the form of ablock diagram an optical disc recorder according to the presentinvention. As shown, the optical disc recorder incorporates the levelindication apparatus 40 to detect and indicate the output level of 1-bitdigital audio signal to be recorded to the SACD.

[0072] The optical disc recorder includes a laser source 31 to emitrecording laser light, light modulator 32 to modulate the laser lightfrom the laser source 31 with recording data which will be described indetail later, sub code signal generator 36, delta-sigma modulator 35 togenerate 1-bit digital audio signal, recording data generator 37 togenerate recording data from the sub code signal and 1-bit audio signal,and a mirror 33 included in a feed mechanism to move the laser lightmodulated by the modulator 32 radially of an optical disc 38 rotated bya spindle moor 39.

[0073] The laser source 31 uses He—Ne gas laser, Ar gas laser or thelike to generate the recording laser light. The recording laser light issupplied to the light modulator 32 where it will be modulated.

[0074] The light modulator 32 is an EOM (electro-optical modulator)whose index of refraction varies depending upon a voltage appliedthereto. It should be noted that an AOM (acousto-optical modulator) ofsuch a type as to generate ultrasounds (compression wave) in a medium bya piezoelectric element may be used instead of the EOM.

[0075] The sib code signal generator 36 generates sub code signal suchas content data or the like and supplies it to the recording datagenerator 37. The recording data generator 37 receives also 1-bitdigital audio signal from the delta-sigma modulator 35.

[0076] As will be seen from FIG. 7, the level indication apparatus 40used in the optical disc recorder as the second embodiment of thepresent invention is constructed similarly to the level indicationapparatus 11 shown in FIG. 3. Namely, it includes a level detector andindicator unit. The level indication apparatus 40 includes the leveldetector 12 constructed as shown in FIG. 7. Since signal level isexamined using a signal modulation factor supplied from the leveldetector 12, no multiplier and adder are required, which leads to asimplified circuit configuration. The level indication apparatus 40according to the present invention is thus simple in circuitconfiguration, and so it can be manufactured with less costs andconsumes less power. Also, the level indication apparatus 40 may not beany dedicated circuit but may be formed from a CPU and its software.Thus, the construction itself will not be complicated, and since theaccuracy of signal processing depends upon the software, a signal levelcan be determined uniquely.

[0077] By providing the aforementioned level indication apparatus 40 inthe optical disc recorder according to the present invention, it can beavoided that when the same music is recorded by a plurality of theoptical disc recorders, the level of the music data is indicated varyingfrom one recorder type to another. Also, by selecting an appropriateparameter for the modulation factor, it is possible to match themodulation factor with an intended frequency band.

[0078] Next, a third embodiment of the present invention will bedescribed.

[0079] The third embodiment is an application of the present inventionto an optical disc editing apparatus incorporating the level indicationapparatus according to the present invention.

[0080] Also in an editing apparatus for producing a medium from whichsignals included in a wide frequency band can be reproduced using sounddata recorded by the recorder as in the recording to the SACD, thesignals should undergo editions such as sound level adjustment,equalization, dynamic ranging and the like. So, unless the sound levelafter edited is monitored, the level of signals inscribed to a disc willbe higher, which may possibly damage the player which plays back thedisc. Since a delicate level adjustment is effected in the soundplayback, the level meter should be accurate.

[0081] To meet the above requirements, the optical disc editingapparatus according to the present invention is constructed as shown inFIG. 9. In the optical disc editing apparatus shown in FIG. 9, audiodata recorded in the SACD is reproduced and the output level of edited1-bit digital signal is detected and displayed by the built-in levelindication apparatus 11.

[0082] The optical disc editing apparatus according to the presentinvention is a combination of the optical disc player shown in FIG. 1,from which the D/A converter 8 is omitted and in which an editingprocessor 18 is additionally provided instead of the D/A converter 8downstream of the audio decoder 5 and the optical disc recorder shown inFIG. 8, of which the delta-sigma modulator 35 is connected to theediting processor 18.

[0083] In the level indication apparatus 11, the level of 1-bit digitalsignal generated by the delta-sigma modulator 35 is detected by thelevel detector 12, and the signal level detected by the level detector12 is indicated in the indicator unit 13. More specifically, the leveldetector 12 is supplied with a sequence of 1-bit digital signals fromthe delta-sigma modulator 35 and counts the number of zeros (0) or ones(1) included in the row of a predetermined number n of 1-bit digitalsignals to detect the level of the 1-bit digital signal.

[0084] Note that the delta-sigma modulator 35 generates 1-bit digitalsignal by the delta-signal modulation of a multi-bit digital signaloutput from the editing processor 18.

[0085] The editing processor 18 makes editions such as sound leveladjustment, equalization, dynamic ranging and the like of 1-bit-digitalsignal decoded by the audio decoder 5 correspondingly to operations of auser's operation unit 14 by the user. The output from the editingprocessor 18 is a multi-bit digital signal. This digital signal isconverted again by the delta-sigma modulator 35 into 1-bit digitalsignal.

[0086] At this time, the level detector 12 in the level indicationapparatus 11 detects the level of the 1-bit digital signal thus edited,and indicates it. Thus, the user can monitor the level of a signalinscribed to the disc, and protect the player which plays the mediumtherein against the aforementioned damage.

[0087] Since the level detector constructed as shown in FIG. 3 or 7examines the level of a signal with the use of a modulation factor forthe signal, the level indication apparatus 11 does not require anymultiplier and adder, which will lead to a simple circuit configuration.Because of such a simplified circuit configuration, the apparatus can bemanufactured with less costs and consumes less power. Also, by using thesignal level detecting method according to the present invention, thelevel indication apparatus 11 may not be any dedicated circuit but maybe formed from a CPU and its software. Thus, the construction itselfwill not be complicated, and since the accuracy of signal processingdepends upon the software, a signal level can be determined uniquely.

[0088] By providing the aforementioned level indication apparatus 11 inthe optical disc editing apparatus according to the present invention,it can be avoided that when the same music is recorded to a plurality ofoptical discs, the level of the music data is indicated varying from onedisc type to another. Also, by selecting an appropriate parameter forthe modulation, it is possible to match the modulation factor with anintended frequency band.

[0089] In each of the aforementioned embodiments of the presentinvention, the signal level detector detects, by the level detector, thelevel of 1-bit digital signal for the purpose of informing the user ofthe level of a signal to be reproduced or recorded, and indicates it inthe indicator unit. The signal level detector according to the presentinvention may be designed such that the level detector will alwaysmonitor the reproduction level of the audio player and automaticallyreduce the Output when a signal whose level is higher than apredetermine one is supplied in order to protect the amplifier andspeaker.

[0090] The signal level detector according to the present invention isalso usable to check the level of electronically filed sound data.Recently, sound data is recorded, reproduced and edited as computer datafile in many cases. To check the level of sound in such a sound file,the signal level detecting method according to the present inventionneeds neither any complicated signal processing nor special hardware andthus can be used to check, only by the CPU and its software, the levelof sound data as an electronic file to see whether any abnormallyhigh-level sound is included in the file without having to reproduce thesound data once.

INDUSTRIAL APPLICABILITY

[0091] As having been described in the foregoing, the signal leveldetecting apparatus and method according to the present invention candetect the level of 1-bit digital signal by a simple, smaller-scalecircuit configuration.

[0092] Also, the signal level indication apparatus according to thepresent invention permits, when applied in a player, recorder andediting apparatus, to avoid that the signal level indication varies fromone apparatus type to another.

1. A signal level detector comprising: a counting means sequentiallysupplied with 1-bit digital signals obtained by the delta-sigmamodulation and which counts the number of zeros (0) or ones (1) in the1-bit digital signal row including a predetermined number of 1-bitdigital signals.
 2. The apparatus as set forth in claim 1, furthercomprising a table of conversion between the number of zeros (0) or ones(1) counted by the counting means and a signal level.
 3. The apparatusas set forth in claim 2, wherein the conversion table has stored thereinthe signal level logarithmically represented and the number of zeros (0)or ones (1) in correspondence with each other.
 4. A signal leveldetecting method comprising steps of: sequentially receiving 1-bitdigital signals obtained by the delta-sigma modulation and counting thenumber of zeros (0) or ones (1) in the 1-bit digital signal rowincluding a predetermined number of 1-bit digital signals; and detectingthe level of the 1-bit digital signal based on the number of zeros (0)or ones (1) counted in the counting step.
 5. The method as set forth inclaim 4, wherein in the level detecting step, the signal level isdetected referring to a conversion table having stored therein thesignal level logarithmically represented and the number of zeros (0) orones (1) in correspondence with each other.
 6. A signal level indicationapparatus comprising: a counting means sequentially supplied with 1-bitdigital signals obtained by the delta-sigma modulation and which countsthe number of zeros (0) or ones (1) in the 1-bit digital signal rowincluding a predetermined number of 1-bit digital signals; and means forindicating the signal level detected based on the counting resultsupplied from the counting means.
 7. The apparatus as set forth in claim6, further comprising a table of conversion between the number of zeros(0) or ones (1) counted by the counting means and a signal level.
 8. Theapparatus as set forth in claim 7, wherein the conversion table hasstored therein the signal level logarithmically represented and thenumber of zeros (0) or ones (1) in correspondence with each other.